john salzer - wesleyan university alfalfa undergraduate workshop

John Salzer - Wesleyan University ALFALFA Undergraduate Workshop Union College 12-13 July 2006

Optical Propertiesof

HI-selected Galaxies

Outline of Talk

• Lessons learned: optical study of the ADBS sample.

• Examples of broad-band images of HI-selected galaxies.

• Properties of the ADBS sample.

• Narrow-band imaging projects.

What will ALFALFA galaxies look like in the optical?

Optical ObservationsOf HI-Selected

Galaxies (ADBS)

The ADBS Survey• The Arecibo Dual Beam Survey (ADBS) was carried out by Rosenberg &

Schneider (2000).

• Drift-scan survey carried out with the Arecibo 305-m telescope. Sample includes 265 galaxies over ~430 sq. deg.

• “Blind” HI survey - does not suffer from optical selection effects. Offers a unique, unbiased look at the gas-rich galaxy population in the local universe.

• Over 30% of the ADBS galaxies not included in ANY galaxy catalog, ~50% fainter than the Updated Zwicky Catalog (UZC) magnitude limit (B = 15.5).

• In many ways the ADBS provides a PREVIEW of ALFALFA! But ALFALFA will be MUCH BETTER: filled survey (7000 sq. deg.) AND better velocity coverage and resolution AND longer effective integration times.

Arecibo Observatory Arecibo, Puerto Rico

305-m Radio Telescope

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Sky coverage of ADBS

The ADBS Survey

The galaxies detected in the ADBS exhibit a broad range of HI masses, with a median value of log(MHI) = 9.21 and a tail extending to values below 108 solar masses.

The ADBS Survey• The Arecibo Dual Beam Survey (ADBS) was carried out by Rosenberg &

Schneider (2000).

• Drift-scan survey carried out with the Arecibo 305-m telescope. Sample includes 265 galaxies over ~430 sq. deg.

• “Blind” HI survey - does not suffer from optical selection effects. Offers a unique, unbiased look at the gas-rich galaxy population in the local universe.

• Over 30% of the ADBS galaxies not included in ANY galaxy catalog, ~50% fainter than the Updated Zwicky Catalog (UZC) magnitude limit (B = 15.5).

• In many ways the ADBS provides a PREVIEW of ALFALFA! But ALFALFA will be MUCH BETTER: filled survey (7000 sq. deg.) AND better velocity coverage and resolution AND longer effective integration times.

• Provides an alternative to more traditional optical galaxy surveys for creating a local census of galaxies.

• Allows for creation of galaxy catalogs that are unbiased by stellar content of objects. Combined with optical catalogs they provide a fairly complete galaxian census.

• “Efficient” way to catalog galaxies: one gets information on redshift, rotation (mass) and total HI content.

• Detect exotic objects, such as HI clouds with no stellar component, tidal features, high velocity clouds, etc.

Why should an optical astronomer care about “blind” HI surveys?

Optical Selection:

Optical magnitude-limited surveys (e.g., the Zwicky Catalog) are good at finding luminous galaxies at modest distances, but are bad at detecting dwarf galaxies much beyond the Local Supercluster.

HI Selection:

HI-selected surveys detect objects based on their HI mass, not their optical output. This opens up the opportunity to detect gas-rich galaxies at large distances, regardless of their stellar content.

The result: the ADBS sample includes lower luminosity galaxies than does the Updated Zwicky Catalog (UZC) magnitude-limited sample (B<15.5) at ALL distances.

HI Selection:

Broad-band Imaging:What to expectFrom ALFALFA







•All Observations shown here have been obtained on the WIYN 0.9m telescope on Kitt Peak.

• This telescope is jointly operated by a consortium of universities that includes Wesleyan.

Example Broad-Band Images of ADBS Galaxies

Bright Spirals


LSB Dwarfs

045254+2310 (a.k.a. the goldfish)

An unusual looking LSB dwarf galaxy from the ADBS sample.



Two VERY low surface brightness ADBS galaxies. Can you see them?

ADBS 023323+2810 ADBS 111032+1932


Is it a star or a galaxy?

The fuzzy “star” is resolved relative to the star just below it (just barely).

This is an ULTRA COMPACT galaxy!

ADBS 113845+2008

?

Spectrum reveals the true nature of ADBS 113845+2008: an ultra-compact star-forming dwarf galaxy.

• B = 16.51• Vhelio = 3105 km/s• MB = -16.65

Properties of theADBS Galaxies

Properties of the ADBS

Apparent magnitudes. Nearly half of the ADBS galaxies have B > 15.5. These fainter galaxies are not included in magnitude-limited catalogs.


Morphological Classifications. The ADBS is a roughly equal mix of spirals andirregulars (including the LSB galaxies). There is a small number of early types and compact objects.


B-V colors. The median color is B-V = 0.47, far bluer than in typical magnitude-limited samples. The dwarf galaxies are particularly blue.


Color vs. Galaxy type. We can investigate the properties of the ADBS galaxies as a function of their galaxy class - in this case B-V color.


Absolute magnitudes. There is a solid component of luminous galaxies included in the ADBS, as well as a large contingent of dwarf systems. The median MB is -18.29.


Central Surface Brightness vs. Luminosity. The major galaxy types are indicated by the plot symbols. There is a clear trend, but with much scatter.

Narrow-Band Imagingof ALFALFA Galaxies

H Imaging of ALFALFA Galaxies

• Availability of SDSS imaging allows us to focus on narrow-band H imaging.

• Complementary to HI data (cold neutral gas, fuel for star formation).

• Use to assess/quantify the total star formation rates in each galaxy.

• Also provide targets for spectroscopy (e.g., Amelie’s thesis).

• Other applications: HII region LFs; distribution of star-forming regions.

ADBS 114921+2607[NGC 3902]

Vel = 3557 km/sMB = -19.83

ADBS 112134+2020[NGC 3646]

Vel = 4335 km/sMB = -22.28

Examples: SpiralsR Band H Narrow Band

Narrow-Band Images of ADBS Galaxies

Examples: DwarfsR Band H Narrow Band

Narrow-Band Images of ADBS Galaxies

ADBS 121206+2518

Vel = 2595 km/sMB = -16.06

ADBS 125850+1308

Vel = 1910 km/sMB = -15.56

Current ALFALFA H Imaging Projects

• Imaging of nearby dwarf galaxies for spectroscopic targets. WIYN 0.9-m (JJS, LvZ) + Wise Obs. 1.0-m (NB) telescopes.

• Measuring the star-formation rate density in the local universe (Wesleyan plus others). WIYN 0.9-m + Wise Obs. 1.0-m telescopes. See ALFALFA projects page!

Spectrum of a metal poor HII region in ADBS 121206+2518. [O/H] < 10% solar.


• Imaging of nearby dwarf galaxies for spectroscopic targets. WIYN 0.9-m (JJS, LvZ) + Wise Obs. 1.0-m (NB) telescopes.


Star Formation Rate Density in the Local Universe

Preliminary ADBS Value

• An important measure of the rate of galaxy formation and evolution over cosmic time is the volume density of star-formation at various epochs (look-back times).

• Previous estimates of the local SFRD have been based on imperfect galaxy samples.

• HI-selected samples like the ALFALFA are perfect for measuring the SFRD, since any galaxy capable of making stars must have a fair amount of gas.

• Our preliminary estimate of the local SFRD based on ADBS data is a factor of two higher than previous estimates!

• Lots of important follow-up work needs to be done!

• Plenty of ways to get yourself or your students involved.

• Talk to one of us if you are interested.

R Band H Narrow BandConclusions:


HI mass-to-light ratio vs Luminosity. We see an inverse relationship between the fractional HI mass (HI mass-to-light ratio) and absolute magnitude such that the more

luminous an object the lower the fractional gas content it will have.

To first order, the ADBS galaxies follow thespatial distribution of the UZC galaxies. This isto no surprise since ~50% of the ADBS galaxies are in the UZC.

Velocity circle diagrams (analogous to cone diagrams) show the UZC galaxies (small dots) and the ADBS galaxies (open circles). RA is “circular”, declination is suppressed and velocity moves outwards. Clusters, filaments and voids can be seen.

Density Environment & Analysis

A weak relationship is seen in the sense that the HI mass in low density environments is slightly greater than in high-density environments. This may be to due to gas stripping in the denser environments.

Density Environment & Analysis

• Sloan Digital Sky Survey (SDSS) cover most/all of ALFALFA-N. This will provide basic photometry (in the SDSS filters) and some surface photometry (deep enough???).

• Very little of ALFALFA-S is covered by SDSS. Will need basic photometric data for most objects fainter than B=15.5 (>50%).

• No current plans for doing SYSTEMATIC broad-band imaging of large portions of ALFALFA, but this could change as projects evolve.

• Targeted observations: Amelie’s dwarfs, deep imaging of HI clouds.

• Other areas with deep, wide field photometry in ALFALFA area: SMUDGES (Liese; Dec = 6 deg); KISS (John; Dec = 30 deg).

Broad-band Follow-up for ALFALFA

Status of ALFALFA SFRD Project

• First observations obtained in Spring ‘06.

• 11 nights on WIYN 0.9-m plus several partial nights on Wise 1.0-m telescope.

• Despite lousy weather, observed 52 objects at WIYN.

• Goal is to obtain high-quality data on 300-500 ALFALFA galaxies over 3-4 years.

• Will lead to most precise estimate of the local SFRD ever produced.


• Imaging of nearby dwarf galaxies for spectroscopic targets. WIYN 0.9-m (JJS) + Wise Obs. 1.0-m (NB) telescopes.


• Imaging of galaxies in selected clusters. San Pedro Martir 2.1-m telescope (PG).

• SMUDGES follow-up. WIYN 0.9-m (LvZ).

john salzer - wesleyan university alfalfa undergraduate workshop

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